The present invention relates to electrical connectors and, more particularly, to a coaxial connector wherein an electrical contact or conductor is captivated or restrained from axial and rotational movement and electrically compensated to improve the voltage standing wave ratio (VSWR) of the connector.
In the past, a significant problem that has been encountered in the coaxial connector field has been to design satisfactory means for captivating the center conductor or contact of the connector against axial and rotational displacement. It has been found that axial and rotational loads may be transmitted to the center contact either directly or indirectly through the coaxial cable causing it to be dislodged or displaced from the dielectric member or core. In other words, the problem manifests itself by the center contact moving axially or rotationally relative to the outer conductor or connector shell. It is well known that axial and rotational loads on the center contact are frequently encountered during normal use of a coaxial connector causing potential signal interference or interruption. Additionally, the problem is aggravated whenever a substantial tension is placed on the cable being joined by the coaxial connector or by thermal shock which can cause relative size changes in the components of the connector.
Other proposed solutions to this problem include utilizing flanges, shoulders, barbs and the like which cooperate with the supporting dielectric member. It will be appreciated that a flange or shoulder extending outwardly from the center conductor creates a change in spacing between the outer conductor or shell and the center conductor creating electrical discontinuities which impair performance. Those skilled in the art have heretofore assumed that coaxial connector performance must always be adversely affected in terms of VSWR by the use of such physical or mechanical retaining means as flanges, shoulders, barbs and the like. It has been recognized that flanges or shoulders have excellent axial retaining capabilities with little or no rotational retaining capability.
In an attempt to overcome the problem of electrical discontinuity while at the same time providing sufficient retaining capabilities, it has been common in the art to secure the center conductor, dielectric member and outer conductor against relative axial and rotational movement by epoxy pinning. This was proposed as a means for retaining the components in a desired relative position of assembly without causing significant electrical discontinuties which might impair the electrical characteristics of a coaxial connector. Epoxy pinning disclosed, for example, in U.S. Pat. No. 3,292,117, has nevertheless proven to be less than completely desirable due in part to the fairly complicated assembly process required.
With epoxy pinning, the surface to be bonded must be clean and free of dirt, oil, grease, tarnish, and other foreign materials to achieve a good bond and a satisfactory seal. This requires solvent cleaning by wiping with a clean, lint-free cloth or a paper wiper moistened with a suitable solvent. The bonding operation then must be performed as soon as possible upon completion of final cleaning to assure that the surface does not become contaminated in the interim. This requires thorough blending at the precise time of need due to the relative short pot life of epoxy. After the epoxy has been applied, it must be heat-cured for several hours and/or room temperature cured for approximately one day.
In order to overcome some of the inherent difficulties with epoxy pinning, physical or mechanical retaining means for the center conductor have been reviewed with a renewed interest. The design must take into consideration that the dielectric member is usually of a relatively smooth and frictionless material such as the synthetic resin polymer sold under the trademark Teflon. It is well appreciated that such a material does not frictionally grip the center conductor adequately to prevent axial and rotational movement of the center conductor relative to the remainder of the coaxial connector especially after repeated engagement and disengagement. Electrical connectors generally, and coaxial connectors in particular, must therefore be designed to minimize the possibility of a shift in the inner conductor or contact of the connector which could result in improper mating and orientation of components causing electrical discontinuities. As a result, any physical or mechanical retaining means for the inner conductor or contact must necessarily embrace all of these considerations.